1. Field of the Invention
The present invention concerns a miniature actuator which is useful in intravascular imaging devices including intravascular ultrasound (IVUS), and optical coherence tomography (OCT). The miniature actuator mechanism and ultrasound or OCT imaging device is embedded in an elongate member such as an intravascular guide wire or catheter to provide imaging guidance in various interventional applications. Also disclosed is a reflector-based ultrasound imaging device created to minimize the overall scale of the imaging device, as well as ultrasound transducers having multiple transducer crystals to increase the field of view of the device while maintaining its small size.
2. Description of the Related Art
Coronary artery disease is very serious and often requires an emergency operation to save lives. The main cause of coronary artery disease is the accumulation of plaques inside artery, which eventually occludes blood vessels. Several solutions are available, e.g., balloon angioplasty, rotational atherectomy, and intravascular stents, to open up the clogged section, which is called stenosis. Traditionally, during the operation, surgeons rely on X-ray fluoroscopic images that are basically planary images showing the external shape of the silhouette of the lumen of blood vessels. Unfortunately, with X-ray fluoroscopic images, there is a great deal of uncertainty about the exact extent and orientation of the atherosclerotic lesions responsible for the occlusion, making it difficult to find the exact location of the stenosis. In addition, though it is known that restenosis can occur at the same place, it is difficult to check the condition inside the vessels after surgery. Similarly, intravascular imaging would prove valuable during interventional procedures as an aid to navigation and for intraoperative feedback. For example, the precise placement and appropriate expansion of stents would benefit from concurrent intravascular imaging. Existing intravascular imaging devices are too large and insufficiently flexible to be placed simultaneously with other devices.
In order to resolve these issues, an ultrasonic transducer device has been utilized for endovascular intervention to visualize the inside of the blood vessels. To date, the current technology is mostly based on one or more stationary ultrasound transducers or rotating a single transducer in parallel to the blood vessels by means of a rotating shaft which extends through the length of the catheter to a motor or other rotary device located outside the patient. These devices have limitations in incorporating other interventional devices into a combination device for therapeutic aspects. They require a large space inside catheter such that there is not enough room to accommodate other interventional devices. Also due to the nature of the rotating shaft, the distal end of the catheter is very stiff and it is hard to go through tortuous arteries. The high speed rotating shaft also contributes to distorted non-uniform images when imaging a tortuous path in the vasculature. OCT has also been utilized to visualize the intravascular space based on differential reflectance, but like the existing ultrasound devices, most rely on a rotating fiber optic which extends along the length of the device. This approach also has problems, including for example the manipulation, spinning and scanning motion required with respect to a delicate glass or polycarbonate optical fiber; the actuator mechanism located outside the patient and tip located inside the patient are significantly distant from one another, leading to inefficiencies and control issues arising from the torque created by a long, spinning member; and remote mechanical manipulation and a long spinning element distort the image due to non-uniform rotational distortion. Given the numerous difficulties with current intravascular imaging devices, there is a need for improved intravascular imaging devices.